Projection system and image color correction method

ABSTRACT

A projection system including a first projection device and a first image capturing device is provided. The first projection device projects a first projection image. The first projection image includes a plurality of different color lights and has color blocks of different brightnesses formed by the plurality of different color lights. The first image capturing device captures the first projection image to generate a first captured image. The first image capturing device includes a first processor. The first processor converts the first captured image into a first converted image according to a first conversion matrix. A color gradation adjustment operation is performed on the first converted image to output an adjustment signal, and the first projection device adjusts the projected first projection image according to the adjustment signal. An image color correction method is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of China application serialno. 201910091608.2, filed on Jan. 30, 2019. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND Technical Field

The invention relates to an optical system and an optical correctionmethod, and particularly relates to a projection system and an imagecolor correction method.

Description of Related Art

A main difference between a projector and a television is that a lightbeam of the projector is first projected onto a wall and then reflectedto human eyes. Color changes perceived by the human eyes may be variedalong with an ambient light source, a color of a projection wall and acolor system of the projector itself. Although a red, green and bluecolor model may intuitively describe any color that can be seen by humaneyes, regarding a human eye perception system, an HSV color model makesit easier for people to understand composition of color: Hue, Saturationand Value. A user control interface of the projector or a TV screen alsocommonly adopts the HSV color model for the user to perform adjustmentand control. People may usually perceive a hue shift or a brightnessdifference of an image projected by the projector.

The projector basically uses mixtures of three color lights to producevarious colors. However, along with aging of optical components in theprojector, or because the effect of a color temperature of an ambientlight source and a color of the projection wall, the projected colorsmay be varied. Therefore, a color system of the projector often needs tobe corrected. Moreover, when several projectors are spliced together,the color systems of different projectors are inconsistent, so thatcolor synchronization among the projectors is also required in order tomake overlapping areas of the projectors to merge perfectly.

The information disclosed in this Background section is only forenhancement of understanding of the background of the describedtechnology and therefore it may contain information that does not formthe prior art that is already known to a person of ordinary skill in theart. Further, the information disclosed in the Background section doesnot mean that one or more problems to be resolved by one or moreembodiments of the invention was acknowledged by a person of ordinaryskill in the art.

SUMMARY

The invention is directed to a projection system and an image colorcorrection method. The projection system performs correction accordingto the image color correction method, so as to provide good imagequality.

Other objects and advantages of the invention may be further illustratedby the technical features broadly embodied and described as follows.

In order to achieve one or a portion of or all of the objects or otherobjects, an embodiment of the invention provides a projection system.The projection system includes a first projection device and a firstimage capturing device. The first projection device is configured toproject a first projection image. The first projection image includes aplurality of different color lights and has color blocks of differentbrightnesses formed by the plurality of different color lights.

The first image capturing device is configured to capture the firstprojection image to generate a first captured image. The first imagecapturing device includes a first processor. The first processorconverts the first captured image into a first converted image accordingto a first conversion matrix. A color gradation adjustment operation isperformed on the first converted image to output an adjustment signal,and the first projection device adjusts the projected first projectionimage according to the adjustment signal.

In order to achieve one or a portion of or all of the objects or otherobjects, another embodiment of the invention provides an image colorcorrection method adapted to a projection system. The image colorcorrection method includes: projecting a first projection image, wherethe first projection image includes a plurality of different colorlights and has color blocks of different brightnesses formed by theplurality of different color lights; capturing the first projectionimage to generate a first captured image; converting the first capturedimage into a first converted image according to a first conversionmatrix; performing a color gradation adjustment operation on the firstconverted image to output an adjustment signal; and adjusting theprojected first projection image according to the adjustment signal.

Based on the above description, the embodiments of the invention have atleast one of following advantages and effects. The projection systemperforms the color gradation adjustment operation on the first convertedimage to output the adjustment signal, and the first projection deviceadjusts the projected first projection image according to the adjustmentsignal, so that the first projection device is adapted to provide goodimage quality.

Other objectives, features and advantages of the present invention willbe further understood from the further technological features disclosedby the embodiments of the present invention wherein there are shown anddescribed preferred embodiments of this invention, simply by way ofillustration of modes best suited to carry out the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a schematic diagram of a projection system according to anembodiment of the invention.

FIG. 2 is a flowchart illustrating an image color correction methodaccording to an embodiment of the invention.

FIG. 3 is a schematic diagram of a projection system according toanother embodiment of the invention.

FIG. 4 is a flowchart illustrating an image color correction methodaccording to another embodiment of the invention.

FIG. 5 is a schematic diagram of a projection system according toanother embodiment of the invention.

FIG. 6 is a flowchart illustrating a conversion matrix generation methodaccording to an embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

It is to be understood that other embodiment may be utilized andstructural changes may be made without departing from the scope of thepresent invention. Also, it is to be understood that the phraseology andterminology used herein are for the purpose of description and shouldnot be regarded as limiting. The use of “including,” “comprising,” or“having” and variations thereof herein is meant to encompass the itemslisted thereafter and equivalents thereof as well as additional items.Unless limited otherwise, the terms “connected,” “coupled,” and“mounted,” and variations thereof herein are used broadly and encompassdirect and indirect connections, couplings, and mountings.

FIG. 1 is a schematic diagram of a projection system according to anembodiment of the invention. Referring to FIG. 1, the projection system100 of the embodiment includes a first projection device 110 and a firstimage capturing device 120 and a system processor 130. The first imagecapturing device 120 includes a first processor 122. In the embodiment,the system processor 130 may be a processor directly embedded in thefirst image capturing device 120, or independently configured outsidethe first image capturing device 120. If the system processor 130 isdirectly embedded in the first image capturing device 120, the systemprocessor 130 is coupled to the first projection device 110; if thesystem processor 130 is a processor independently configured outside thefirst image capturing device 120, the system processor 130 isrespectively coupled to the first projection device 110 and the firstimage capturing device 120. When the system processor 130 is embedded inthe first image capturing device 120, the system processor 130 may be aprocessor the same with or different to the first processor 122. Whenthe system processor 130 is independently configured outside the firstimage capturing device 120, the system processor 130 is, for example,disposed in a host system. The host system is, for example, a desktopcomputer, a notebook computer or a mobile device, etc., that has acomputation function. In the embodiment, the first image capturingdevice 120 is unnecessarily to be embedded in the first projectiondevice 110.

The first projection device 110 is configured to project a firstprojection image IP1 onto a projection plane 140 such as a wall or ascreen, etc. The first projection image IP1 comprises a plurality ofdifferent color lights. The first projection image IP1 has a checkerpattern with a plurality of color blocks 152 formed by the differentcolor lights. Each of the color blocks 152 is formed through projectionof a different color light with a different brightness, so that thecolor blocks 152 have different colors, and the brightness of each colorlight is different. In the embodiment, the first projection device 110,for example, projects the first projection image IP1 with seven colorlights of red, yellow, green, cyan, blue, magenta, white and sixbrightnesses respectively presented by the seven color lights, so that anumber of the color blocks 152 formed by the different color lights indifferent brightnesses is 42, though the invention is not limitedthereto.

The first image capturing device 120 is configured to capture the firstprojection image IP1 projected to the projection plane 140 to generate afirst captured image IC1, and the first captured image IC1 istransmitted to the first processor 122. In the embodiment, an imagecapturing range of the first image capturing device 120 is, for example,greater than or equal to a projection range of the first projectiondevice 110. The first processor 122 converts the first captured imageIC1 into a first converted image IJ1 according to a first conversionmatrix T1. In the embodiment, the first conversion matrix T1 is, forexample, a conversion matrix generated base on a correction color card K(shown in FIG. 5), and is pre-stored in the first image capturing device120. However, the invention does not limit a generation mode of thefirst conversion matrix T1. The first converted image IJ1 is an imageclose to human eye perception.

The system processor 130 is configured to receive the first convertedimage IJ1 from the first processor 1122 of the first image capturingdevice 120, and performs a color gradation adjustment operation on thefirst converted image IJ1 to output an adjustment signal S1 to the firstprojection device 110. The first projection device 110 adjusts theprojected first projection image P1 according to the adjustment signalS1. In the embodiment, the color gradation adjustment operation includesa hue adjustment operation and a value adjustment operation.

Before the system processor 130 performs the hue adjustment operationand the value adjustment operation, the system processor 130 firstconverts each color light of the first converted image IJ1 from a RGBcolor space to an HSV color space. Taking red color light as an example,a following matrix conversion represents that the red color light of thefirst converted image IJ1 is converted from the RGB color space to theHSV color space:

$\left. \begin{bmatrix}{J_{C\; 1}^{R}\left( {1,r} \right)} & {J_{C\; 1}^{G}\left( {1,r} \right)} & {J_{C\; 1}^{B}\left( {1,r} \right)} \\{J_{C\; 1}^{R}\left( {2,r} \right)} & {J_{C\; 1}^{G}\left( {2,r} \right)} & {J_{C\; 1}^{B}\left( {2,r} \right)} \\\vdots & \vdots & \vdots \\{J_{C\; 1}^{R}\left( {6,r} \right)} & {J_{C\; 1}^{G}\left( {6,r} \right)} & {J_{C\; 1}^{B}\left( {6,r} \right)}\end{bmatrix}\rightarrow\begin{bmatrix}{J_{C\; 1}^{H}\left( {1,r} \right)} & {J_{C\; 1}^{S}\left( {1,r} \right)} & {J_{C\; 1}^{V}\left( {1,r} \right)} \\{J_{C\; 1}^{H}\left( {2,r} \right)} & {J_{C\; 1}^{S}\left( {2,r} \right)} & {J_{C\; 1}^{V}\left( {2,r} \right)} \\\vdots & \vdots & \vdots \\{J_{C\; 1}^{H}\left( {6,r} \right)} & {J_{C\; 1}^{S}\left( {6,r} \right)} & {J_{C\; 1}^{V}\left( {6,r} \right)}\end{bmatrix} \right.$

Where, r in each element J^(X1) _(C1)(i,r) in the matrix represents thered color light, i is an integer from 1 to 6, which represents that thesix color blocks formed by red color light with different brightnesses,X1 represents each coordinate axis of different color spaces of R, G, B,H, S or V. Matrix conversion representations of other color lights maybe deduced by analogy.

Then, the system processor 130 performs the hue adjustment operation onthe first converted image IJ in the HSV color space. In the hueadjustment operation, the system processor 130 obtains an average hue ofeach color light in the first converted image IJ1, and calculates adifference between the average hue of each color light and a respectivestandard hue. Taking the red color light as an example, the systemprocessor 130 calculates an average hue m(H,r) of 6 brightnesses of thered color light. Regarding the red color light, a correct hue should be0. If m(H,r)>0, the hue of the red color light subtracts m(H,r). If m(H,r)<0, the hue of the red color light is added with m(H,r). Therefore,the system processor 130 may calculate a hue compensation value of thered color light. Hue compensation values of other color lights may beobtained in the same way.

On the other hand, the system processor 130 performs the valueadjustment operation on the first converted image IJ1 in the HSV colorspace. In the value adjustment operation, the system processor 130 takesthe minimum value of each brightness in all color lights of the firstconverted image IJ1, and calculates a compensation value of each colorlight of the first converted image IJ1 in such brightness based on theminimum value of this brightness. In the embodiment, the systemprocessor 130 further distinguishes a red component w^(R), a greencomponent w^(G) and a blue component w^(B) from a white color light, andthe system processor 130 adjusts the brightnesses of 9 color lights. Thefollowing matrix represents the brightnesses of 9 color lights:

$\begin{bmatrix}{J_{C\; 1}^{V}\left( {1,r} \right)} & {J_{C\; 1}^{V}\left( {1,y} \right)} & {J_{C\; 1}^{V}\left( {1,g} \right)} & {J_{C\; 1}^{V}\left( {1,c} \right)} & {J_{C\; 1}^{V}\left( {1,b} \right)} & {J_{C\; 1}^{V}\left( {1,m} \right)} & {J_{C\; 1}^{V}\left( {1,w^{R}} \right)} & {J_{C\; 1}^{V}\left( {1,w^{G}} \right)} & {J_{C\; 1}^{V}\left( {1,w^{B}} \right)} \\{J_{C\; 1}^{V}\left( {2,r} \right)} & {J_{C\; 1}^{V}\left( {2,y} \right)} & {J_{C\; 1}^{V}\left( {2,g} \right)} & {J_{C\; 1}^{V}\left( {2,c} \right)} & {J_{C\; 1}^{V}\left( {2,b} \right)} & {J_{C\; 1}^{V}\left( {2,m} \right)} & {J_{C\; 1}^{V}\left( {2,w^{R}} \right)} & {J_{C\; 1}^{V}\left( {2,w^{G}} \right)} & {J_{C\; 1}^{V}\left( {2,w^{B}} \right)} \\{J_{C\; 1}^{V}\left( {3,r} \right)} & {J_{C\; 1}^{V}\left( {3,y} \right)} & {J_{C\; 1}^{V}\left( {3,g} \right)} & {J_{C\; 1}^{V}\left( {3,c} \right)} & {J_{C\; 1}^{V}\left( {3,b} \right)} & {J_{C\; 1}^{V}\left( {3,m} \right)} & {J_{C\; 1}^{V}\left( {3,w^{R}} \right)} & {J_{C\; 1}^{V}\left( {3,w^{G}} \right)} & {J_{C\; 1}^{V}\left( {3,w^{B}} \right)} \\{J_{C\; 1}^{V}\left( {4,r} \right)} & {J_{C\; 1}^{V}\left( {4,y} \right)} & {J_{C\; 1}^{V}\left( {4,g} \right)} & {J_{C\; 1}^{V}\left( {4,c} \right)} & {J_{C\; 1}^{V}\left( {4,b} \right)} & {J_{C\; 1}^{V}\left( {4,m} \right)} & {J_{C\; 1}^{V}\left( {4,w^{R}} \right)} & {J_{C\; 1}^{V}\left( {4,w^{G}} \right)} & {J_{C\; 1}^{V}\left( {4,w^{B}} \right)} \\{J_{C\; 1}^{V}\left( {5,r} \right)} & {J_{C\; 1}^{V}\left( {5,y} \right)} & {J_{C\; 1}^{V}\left( {5,g} \right)} & {J_{C\; 1}^{V}\left( {5,c} \right)} & {J_{C\; 1}^{V}\left( {5,b} \right)} & {J_{C\; 1}^{V}\left( {5,m} \right)} & {J_{C\; 1}^{V}\left( {5,w^{R}} \right)} & {J_{C\; 1}^{V}\left( {5,w^{G}} \right)} & {J_{C\; 1}^{V}\left( {5,w^{B}} \right)} \\{J_{C\; 1}^{V}\left( {6,r} \right)} & {J_{C\; 1}^{V}\left( {6,y} \right)} & {J_{C\; 1}^{V}\left( {6,g} \right)} & {J_{C\; 1}^{V}\left( {6,c} \right)} & {J_{C\; 1}^{V}\left( {6,b} \right)} & {J_{C\; 1}^{V}\left( {6,m} \right)} & {J_{C\; 1}^{V}\left( {6,w^{R}} \right)} & {J_{C\; 1}^{V}\left( {6,w^{G}} \right)} & {J_{C\; 1}^{V}\left( {6,w^{B}} \right)}\end{bmatrix}\quad$

Where the elements J^(V) _(C1)(i,

) in the matrix represent brightnesses of all of the color lights, i isan integer from 1 to 6, which represents that each color light has 6color blocks formed by each color light with different brightnesses,

is r, y, g, c, b, m, w^(R), w^(G) or w^(B), which respectivelyrepresents 9 color lights of red color light, yellow color light, greencolor light, cyan color light, blue color light, magenta color light,red component of the white color light, green component of the whitecolor light and blue component of the white color light.

Taking a first brightness (i.e. i=1, a first row in the matrix) as anexample, the system processor 130 may obtain the minimum value min{J^(V) _(C1)(1,

)} of the first brightness from all of the color lights. In this way,the system processor 130 may obtain the minimum value min{J^(V) _(C1)(i,

)} of each brightness, where i is an integer from 1 to 6. Taking the redcolor light as an example, the system processor 130 may calculate abrightness compensation value of the red color light:

$\frac{1}{6}{\sum\limits_{i = 1}^{6}\;{\frac{\min\left\{ {J_{C\; 1}^{V}\left( {i,\ell} \right)} \right\}}{J_{C\; 1}^{V}\left( {i,r} \right)}.}}$Brightness compensation values of the other color lights may be deducedby analogy.

In the embodiment, the system processor 130 performs the color gradationadjustment operation on the first converted image IJ1 so as to outputthe adjustment signal S1 to the first projection device 110. Theadjustment signal S1 includes a hue compensation value and a brightnesscompensation value of each color light. The first projection device 110adjusts the projected first projection image IP1 according to the huecompensation value and the brightness compensation value of theadjustment signal S1. In the embodiment, before the first projectionimage IP1 is adjusted, the brightness of the first projection image IP1projected by the first projection device 110 is already the maximumbrightness, so that when the first projection device 110 adjusts theprojected first projection image IP1 according to the brightnesscompensation value, first projection device 110 decreases the brightnessof each color light to implement the adjustment. In this way, theprojection image projected from the first projection device 110 does notvary in image color due to the effects of a color temperature of anambient light source and a color of a projection wall surface.

In the embodiment, in case that a framework of the first projectiondevice 110 is not changed, the first image capturing device 120 is addedto perform color correction on the image projected from the firstprojection device 110, and the image color correction performed on thefirst projection device 110 is to adjust hue values and brightnessvalues of different color lights.

FIG. 2 is a flowchart illustrating an image color correction methodaccording to an embodiment of the invention. Referring to FIG. 1 andFIG. 2, the image color correction method of the embodiment is at leastadapted to the projection system 100 of FIG. 1, though the invention isnot limited thereto. Taking the projection system 100 of FIG. 1 as anexample, in a step S100, the first projection device 110 projects thefirst projection image IP1. In a step S110, the first image capturingdevice 120 captures the first projection image IP1 to generate the firstcaptured image IC1. In a step S120, the first processor 122 of the firstimage capturing device 120 converts the first captured image IC1 intothe first converted image IJ1 according to the first conversion matrixT1. In a step S130, the system processor 130 performs a color gradationadjustment operation on the first converted image IJ1 to output theadjustment signal S1. In a step S140, the first projection device 110adjusts the projected first projection image IP1 according to theadjustment signal S1. Moreover, enough instructions, recommendations andimplementation descriptions for the image color correction method of theinvention may be learned from the description of the embodiment of FIG.1, and detail thereof is not repeated.

FIG. 3 is a schematic diagram of a projection system according toanother embodiment of the invention. Referring to FIG. 1 and FIG. 3, theprojection system 200 of the embodiment is similar to the projectionsystem of FIG. 1, and a main difference there between is that theprojection system 200 further includes a second projection device 210and a second image capturing device 220. The second image capturingdevice 220 includes a second processor 222. In the embodiment, thesystem processor 130 may be directly embedded in the first imagecapturing device 120 or the second image capturing device 220, orindependently disposed outside the first image capturing device 120 orthe second image capturing device 220. When the system processor 130 isdisposed in the second image capturing device 220, the system processor130 may be the same or different to the second processor 222.

In the embodiment, the system processor 130, the first processor 122 andthe second processor 222 are processors having computation capability.Alternatively, the system processor 130, the first processor 122 and thesecond processor 222 may be hardware circuits designed through aHardware Description Language (HDL) or any other digital circuit designmethod well known by those skilled in the art, and implemented through aField Programmable Gate Array (FPGA), a Complex Programmable LogicDevice (CPLD) or an Application-specific Integrated Circuit (ASIC).

In the embodiment, the second projection device 210 projects a secondprojection image IP2 to the projection plane 140. The second imagecapturing device 220 captures the second projection image IP2. Thesecond processor 222 of the second image capturing device 220 converts asecond captured image IC2 into a second converted image IJ2 according toa second conversion matrix T2. The system processor 130 receives thefirst converted image IJ1 transmitted from the first processor 122 andthe second converted image IJ2 transmitted from the second processor222. The system processor 130 not only performs the color gradationadjustment operation on the first converted image IJ1, but also performsthe color gradation adjustment operation on the second converted imageIJ2, so as to respectively output the adjustment signal S1 and anadjustment signal S2 to the first projection device 110 and the secondprojection device 210.

In the embodiment, the method that the system processor 130 performs thehue adjustment operation on the first converted image IJ1 is the samewith that of the embodiment of FIG. 1. The method that the systemprocessor 130 performs the hue adjustment operation on the secondconverted image IJ2 is the similar with that of the embodiment ofFIG. 1. In the embodiment, the system processor 130 synchronouslyperforms value adjustment operation on the first converted image IJ1 andthe second converted image IJ2.

To be specific, in the value adjustment operation, the system processor130 obtains the minimum value of each brightness from all color lightsof the first converted image IJ1 and the second converted image IJ2, andcalculates a compensation value of each color light of the firstconverted image IJ1 and the second converted image IJ2 in suchbrightness based on the minimum value of this brightness. Taking a firstbrightness as an example, the system processor 130 may obtain theminimum value min {J^(V) _(C1)(1,

), J^(V) _(C2)(1,

)} from the first brightness in all of the color lights. In this way,the system processor 130 may obtain the minimum value min {J^(V)_(C1)(i,

), J^(V) _(C2)(i,

)} of each brightness, where i=1-6. Taking the red color light as anexample, the system processor 130 may respectively calculate abrightness compensation value of the red color light of the firstprojection device 110:

$\frac{1}{6}{\sum\limits_{i = 1}^{6}\;\frac{\min\left\{ {{J_{C\; 1}^{V}\left( {i,\ell} \right)},{J_{C\; 2}^{V}\left( {i,\ell} \right)}} \right\}}{J_{C\; 1}^{V}\left( {i,r} \right)}}$and a brightness compensation value of the red color light of the secondprojection device 210:

$\frac{1}{6}{\sum\limits_{i = 1}^{6}\;{\frac{\min\left\{ {{J_{C\; 1}^{V}\left( {i,\ell} \right)},{J_{C\; 2}^{V}\left( {i,\ell} \right)}} \right\}}{J_{C\; 1}^{V}\left( {i,r} \right)}.}}$Brightness compensation values of the other color lights may be deducedby analogy.

In the embodiment, the system processor 130 performs the color gradationadjustment operation on the first converted image IJ1 so as to outputthe adjustment signal S1 to the first projection device 110. Theadjustment signal S1 includes a hue compensation value and a brightnesscompensation value of each color light of the first projection device110. The first projection device 110 adjusts the projected firstprojection image IP1 according to the hue compensation value and thebrightness compensation value of the adjustment signal S1. On the otherhand, the system processor 130 performs the color gradation adjustmentoperation on the second converted image IJ2 so as to output theadjustment signal S2 to the second projection device 120. The adjustmentsignal S2 includes a hue compensation value and a brightnesscompensation value of each color light of the second projection device120. The second projection device 120 adjusts the projected secondprojection image IP2 according to the hue compensation value and thebrightness compensation value of the adjustment signal S2.

In the embodiment, since the system processor 130 may synchronouslyperform the value adjustment operation on the first converted image IJ1and the second converted image IJ2, the colors of two or more projectiondevices may be synchronized, so as to conform the color performances ofthe projection devices. The image color correction method of theembodiment takes two projection devices as an example, but is notlimited to two projection devices. Therefore, the projection system 200may perform color correction on different projection devices accordingto different ambient light sources or projection planes, so as toimprove the usage rate of the projection devices.

FIG. 4 is a flowchart illustrating an image color correction methodaccording to another embodiment of the invention. Referring to FIG. 3and FIG. 4, the image color correction method of the embodiment is atleast adapted to the projection system 200 of FIG. 3, though theinvention is not limited thereto. Taking the projection system 200 ofFIG. 3 as an example, in a step S200, the first projection device 110and the second projection device 210 respectively project the firstprojection image IP1 and the second projection image IP2. In a stepS210, the first image capturing device 120 and the second imagecapturing device 220 respectively captures the first projection imageIP1 and the second projection image IP2 to generate a first capturedimage IC1 and a second captured image IC2.

In a step S220, the first processor 122 of the first image capturingdevice 120 and the second processor 222 of the second image capturingdevice 220 respectively convert the first captured image IC1 and thesecond captured image IC2 into the first converted image IJ1 and thesecond converted image IJ2 according to the first conversion matrix T1and the second conversion matrix T2. In a step S230, the systemprocessor 130 synchronously performs the color gradation adjustmentoperation on the first converted image IJ1 and the second convertedimage IJ2 to output the adjustment signal S1 and the adjustment signalS2. In a step S240, the first projection device 110 receives theadjustment signal S1 from the system processor 130, and the secondprojection device 210 receives the adjustment signal S2 from the systemprocessor 130. The first projection device 110 and the second projectiondevice 210 respectively adjust the projected first projection image IP1and the second projection image IP2 according to the adjustment signalS1 and the adjustment signal S2. Moreover, enough instructions,recommendations and implementation descriptions for the image colorcorrection method of the invention may be learned from the descriptionof the embodiments of FIG. 1 and FIG. 3, and detail thereof is notrepeated.

A method of producing the first conversion matrix T1 and the secondconversion matrix T2 is described below. FIG. 5 is a schematic diagramof a projection system according to another embodiment of the invention.The projection system 300 of the embodiment includes the first imagecapturing device 120, the second image capturing device 220 and a thirdimage capturing device 320. The third image capturing device 320 is, forexample, a single lens reflex camera, which has been calibrated. Thefirst image capturing device 120 and the second image capturing device220 are respectively coupled to the third image capturing device 320.

In the embodiment, the ambient light source is set under a standard D65light source, and a color temperature thereof is 6500K, though theinvention is not limited thereto. Under such ambient light source, thethird image capturing device 320 captures an image of the correctioncolor card K to generate a reference image IF. The first image capturingdevice 120 captures the image of the correction color card K to generatea first captured image IC1 to be corrected. The second image capturingdevice 220 captures the image of the correction color card K to generatea second captured image IC2 to be corrected. In the embodiment, thecorrection color card K, for example, has 24 color blocks, as shown inFIG. 5. The correction color card K is often used in professionalphotography, which usually contains 24 printing colors but is notlimited to these colors, as long as it covers as many different colorsas possible in the gamut.

The method that first processor 122 of the first image capturing device120 generates the first conversion matrix T1 according to the referenceimage IF coming from the third image capturing device 320 and the firstcaptured image IC1 to be corrected is, for example, based on a followingequation:

${\begin{bmatrix}{I_{C\; 1}^{R}(1)} & {I_{C\; 1}^{G}(1)} & {I_{C\; 1}^{B}(1)} \\{I_{C\; 1}^{R}(2)} & {I_{C\; 1}^{G}(2)} & {I_{C\; 1}^{B}(2)} \\\vdots & \vdots & \vdots \\{I_{C\; 1}^{R}(24)} & {I_{C\; 1}^{G}(24)} & {I_{C\; 1}^{B}(24)}\end{bmatrix}T\; 1} = \begin{bmatrix}{I_{F}^{R}(1)} & {I_{F}^{G}(1)} & {I_{F}^{B}(1)} \\{I_{F}^{R}(2)} & {I_{F}^{G}(2)} & {I_{F}^{B}(2)} \\\vdots & \vdots & \vdots \\{I_{F}^{R}(24)} & {I_{F}^{G}(24)} & {I_{F}^{B}(24)}\end{bmatrix}$

Where, I^(R) _(C1)(x), I^(G) _(C1)(x), I^(B) _(C1)(x) represent RGBvalues of the first captured image IC1 to be corrected corresponding toeach color block on the correction color card K. I^(R) _(F)(x), I^(B)_(F)(x), I^(B) _(F)(x) represent RGB values of the reference image IFcorresponding to each color block on the correction color card K, and xis an integer from 1 to 24. The method that the second processor 222 ofthe second image capturing device 220 generates the second conversionmatrix T2 according to the reference image IF coming from the thirdimage capturing device and the second image to be corrected IC2 may bededuced by analogy.

In another embodiment, the projection system may only include the firstimage capturing device 120 and the third image capturing device 320 togenerate the first conversion matrix T1. In another embodiment, theprojection system may only include the second image capturing device 220and the third image capturing device 320 to generate the secondconversion matrix T2. The method of generating the first conversionmatrix T1 and the second conversion matrix T2 is not limited by theinvention.

FIG. 6 is a flowchart illustrating a conversion matrix generation methodaccording to an embodiment of the invention. Referring to FIG. 5 andFIG. 6, the conversion matrix generation method of the embodiment is atleast adapted to the projection system 300 of FIG. 5, though theinvention is not limited thereto. Taking the projection system 300 ofFIG. 5 as an example, in a step S300, the third image capturing device320 captures an image of the correction color card K to generate thereference image IF. In a step S310, the first image capturing device 120and the second image capturing device 220 respectively capture the imageof the correction color card K to respectively generate the firstcaptured image IC1 to be corrected and the second captured image IC2 tobe corrected. In a step S320, the first processor 122 generates thefirst conversion matrix T1 according to the reference image IF and thefirst captured image IC1 to be corrected, and the second processor 222generates the second conversion matrix T2 according to the referenceimage IF and the second captured image IC2 to be corrected. Moreover,enough instructions, recommendations and implementation descriptions forthe image color correction method of the invention may be learned fromthe description of the embodiment of FIG. 5, and detail thereof is notrepeated.

In summary, the embodiments of the invention have at least one offollowing advantages and effects. Since the system processor maysynchronously perform the value adjustment operation on the firstconverted image and the second converted image, colors of the two ormore projection devices may be synchronized. The image color correctionmethod of the invention takes two projection devices as an example, butis not limited to two projection devices. Therefore, the projectionsystem may perform image color correction on different projectiondevices according to different ambient light sources or projectionplanes, so as to improve the usage rate of the projection devices.Moreover, image color corrections of two projection devices areperformed based on a same image capturing device (for example, a singlelens reflex camera), so that image color correction among multipleprojection devices may be implemented, which avails stitching of theprojection devices.

The foregoing description of the preferred embodiments of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform or to exemplary embodiments disclosed. Accordingly, the foregoingdescription should be regarded as illustrative rather than restrictive.Obviously, many modifications and variations will be apparent topractitioners skilled in this art. The embodiments are chosen anddescribed in order to best explain the principles of the invention andits best mode practical application, thereby to enable persons skilledin the art to understand the invention for various embodiments and withvarious modifications as are suited to the particular use orimplementation contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and their equivalentsin which all terms are meant in their broadest reasonable sense unlessotherwise indicated. Therefore, the term “the invention”, “the presentinvention” or the like does not necessarily limit the claim scope to aspecific embodiment, and the reference to particularly preferredexemplary embodiments of the invention does not imply a limitation onthe invention, and no such limitation is to be inferred. The inventionis limited only by the spirit and scope of the appended claims. Theabstract of the disclosure is provided to comply with the rulesrequiring an abstract, which will allow a searcher to quickly ascertainthe subject matter of the technical disclosure of any patent issued fromthis disclosure. It is submitted with the understanding that it will notbe used to interpret or limit the scope or meaning of the claims. Anyadvantages and benefits described may not apply to all embodiments ofthe invention. It should be appreciated that variations may be made inthe embodiments described by persons skilled in the art withoutdeparting from the scope of the present invention as defined by thefollowing claims. Moreover, no element and component in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element or component is explicitly recited in the followingclaims.

What is claimed is:
 1. A projection system, comprising: a firstprojection device, configured to project a first projection image,wherein the first projection image comprises a plurality of differentcolor lights and has color blocks of different brightnesses formed bythe plurality of different color lights; and a first image capturingdevice, configured to capture the first projection image to generate afirst captured image, wherein the first image capturing device comprisesa first processor, wherein the first processor converts the firstcaptured image into a first converted image according to a firstconversion matrix; and a second image capturing device, configured tocapture an image of a correction color card to generate a referenceimage, wherein the first image capturing device captures the image ofthe correction color card to generate a first captured image to becorrected, and the first processor generates the first conversion matrixaccording to the reference image and the first captured image to becorrected, wherein a color gradation adjustment operation is performedon the first converted image to output an adjustment signal, and thefirst projection device adjusts the projected first projection imageaccording to the adjustment signal.
 2. The projection system as claimedin claim 1, further comprising a system processor configured to receivethe first converted image to execute the color gradation adjustmentoperation.
 3. The projection system as claimed in claim 2, wherein whenthe system processor performs the color gradation adjustment operation,the system processor converts each color light of the first convertedimage from a RGB color space to an HSV color space, and the colorgradation adjustment operation comprises a hue adjustment operation anda value adjustment operation.
 4. The projection system as claimed inclaim 3, wherein when the system processor performs the hue adjustmentoperation, the system processor takes an average hue of each color lightin the first converted image, and calculates a difference between theaverage hue of each color light and a respective standard hue.
 5. Theprojection system as claimed in claim 4, wherein when the systemprocessor performs the value adjustment operation, the system processortakes the minimum value of each brightness from all color lights of thefirst converted image, and calculates a compensation value of each colorlight of the first converted image in such brightness based on theminimum value of this brightness.
 6. The projection system as claimed inclaim 4, further comprising: a second projection device, configured toproject a second projection image, wherein the second projection imagecomprises a plurality of different color lights and has color blocks ofdifferent brightnesses formed by the plurality of different colorlights; and a third image capturing device, configured to capture thesecond projection image to generate a second captured image, wherein thethird image capturing device comprises a second processor, wherein thesecond processor converts the second captured image into a secondconverted image according to a second conversion matrix; wherein thecolor gradation adjustment operation is performed on the secondconverted image to output the adjustment signal, and the secondprojection device adjusts the projected second projection imageaccording to the adjustment signal.
 7. The projection system as claimedin claim 6, wherein the system processor receives the second convertedimage to execute the color gradation adjustment operation.
 8. Theprojection system as claimed in claim 7, wherein when the systemprocessor performs the color gradation adjustment operation, the systemprocessor converts each color light of the second converted image fromthe RGB color space to the HSV color space.
 9. The projection system asclaimed in claim 8, wherein when the system processor performs the hueadjustment operation, the system processor takes an average hue of eachcolor light in the second converted image, and calculates a differencebetween the average hue of each color light and a respective standardhue.
 10. The projection system as claimed in claim 9, wherein when thesystem processor performs the value adjustment operation, the systemprocessor takes the minimum value of each brightness from all colorlights of the first converted image and the second converted image, andcalculates a compensation value of each color light of the firstconverted image and the second converted image in such brightness basedon the minimum value of this brightness.
 11. The projection system asclaimed in claim 6, wherein third image capturing device captures theimage of the correction color card to generate a second captured imageto be corrected, and the second processor generates the secondconversion matrix according to the reference image and the secondcaptured image to be corrected.
 12. An image color correction method,adapted to a projection system, the image color correction methodcomprising: projecting a first projection image, wherein the firstprojection image comprises a plurality of different color lights and hascolor blocks of different brightnesses formed by the plurality ofdifferent color lights; capturing the first projection image to generatea first captured image; capturing an image of a correction color card togenerate a reference image; capturing the image of the correction colorcard to generate a first captured image to be corrected; generating afirst conversion matrix according to the reference image and the firstcaptured image to be corrected; converting the first captured image intoa first converted image according to the first conversion matrix;performing a color gradation adjustment operation on the first convertedimage to output an adjustment signal; and adjusting the projected firstprojection image according to the adjustment signal.
 13. The image colorcorrection method as claimed in claim 12, wherein the step of performingthe color gradation adjustment operation comprises: converting eachcolor light of the first converted image from a RGB color space to anHSV color space, wherein the color gradation adjustment operationcomprises a hue adjustment operation and a value adjustment operation.14. The image color correction method as claimed in claim 13, whereinthe step of performing the hue adjustment operation comprises: taking anaverage hue of each color light in the first converted image, andcalculating a difference between the average hue of each color light anda respective standard hue.
 15. The image color correction method asclaimed in claim 14, wherein when the step of performing the valueadjustment operation comprises: taking the minimum value of eachbrightness from all color lights of the first converted image, andcalculating a compensation value of each color light of the firstconverted image in such brightness based on the minimum value of thisbrightness.
 16. The image color correction method as claimed in claim14, further comprising: projecting a second projection image, whereinthe second projection image comprises a plurality of different colorlights and has color blocks of different brightnesses formed by theplurality of different color lights; capturing the second projectionimage to generate a second captured image; converting the secondcaptured image into a second converted image according to a secondconversion matrix; performing the color gradation adjustment operationon the second converted image to output the adjustment signal; andadjusting the projected second projection image according to theadjustment signal.
 17. The image color correction method as claimed inclaim 16, wherein the step of performing the color gradation adjustmentoperation comprises: converting each color light of the second convertedimage from the RGB color space to the HSV color space.
 18. The imagecolor correction method as claimed in claim 17, wherein the step ofperforming the hue adjustment operation comprises: taking an average hueof each color light in the second converted image, and calculating adifference between the average hue of each color light and a respectivestandard hue.
 19. The image color correction method as claimed in claim18, wherein the step of performing the value adjustment operationcomprises: taking the minimum value of each brightness from all colorlights of the first converted image and the second converted image, andcalculating a compensation value of each color light of the firstconverted image and the second converted image in such brightness basedon the minimum value of this brightness.
 20. The image color correctionmethod as claimed in claim 16, further comprising: capturing the imageof the correction color card to generate a second captured image to becorrected; generating the second conversion matrix according to thereference image and the second captured image to be corrected.
 21. Aprojection system, comprising: a first projection device, configured toproject a first projection image, wherein the first projection imagecomprises a plurality of different color lights and has color blocks ofdifferent brightnesses formed by the plurality of different colorlights; and a first image capturing device, configured to capture thefirst projection image to generate a first captured image, wherein thefirst image capturing device comprises a first processor, and the firstprocessor converts the first captured image into a first converted imageaccording to a first conversion matrix, wherein a color gradationadjustment operation is performed on the first converted image to outputan adjustment signal, and the first projection device adjusts theprojected first projection image according to the adjustment signal; asystem processor configured to receive the first converted image toexecute the color gradation adjustment operation, wherein when thesystem processor performs the color gradation adjustment operation, thesystem processor converts each color light of the first converted imagefrom a RGB color space to an HSV color space, and the color gradationadjustment operation comprises a hue adjustment operation and a valueadjustment operation, wherein when the system processor performs the hueadjustment operation, the system processor takes an average hue of eachcolor light in the first converted image, and calculates a differencebetween the average hue of each color light and a respective standardhue; a second projection device, configured to project a secondprojection image, wherein the second projection image comprises aplurality of different color lights and has color blocks of differentbrightnesses formed by the plurality of different color lights; and asecond image capturing device, configured to capture the secondprojection image to generate a second captured image, wherein the secondimage capturing device comprises a second processor, and the secondprocessor converts the second captured image into a second convertedimage according to a second conversion matrix, wherein the colorgradation adjustment operation is performed on the second convertedimage to output the adjustment signal, and the second projection deviceadjusts the projected second projection image according to theadjustment signal, wherein the system processor receives the secondconverted image to execute the color gradation adjustment operation,wherein when the system processor performs the color gradationadjustment operation, the system processor converts each color light ofthe second converted image from the RGB color space to the HSV colorspace, wherein when the system processor performs the hue adjustmentoperation, the system processor takes an average hue of each color lightin the second converted image, and calculates a difference between theaverage hue of each color light and a respective standard hue, whereinwhen the system processor performs the value adjustment operation, thesystem processor takes the minimum value of each brightness from allcolor lights of the first converted image and the second convertedimage, and calculates a compensation value of each color light of thefirst converted image and the second converted image in such brightnessbased on the minimum value of this brightness.
 22. An image colorcorrection method, adapted to a projection system, the image colorcorrection method comprising: projecting a first projection image,wherein the first projection image comprises a plurality of differentcolor lights and has color blocks of different brightnesses formed bythe plurality of different color lights; capturing the first projectionimage to generate a first captured image; converting the first capturedimage into a first converted image according to a first conversionmatrix; performing a color gradation adjustment operation on the firstconverted image to output an adjustment signal, wherein the step ofperforming the color gradation adjustment operation comprises:converting each color light of the first converted image from a RGBcolor space to an HSV color space, wherein the color gradationadjustment operation comprises a hue adjustment operation and a valueadjustment operation, wherein the step of performing the hue adjustmentoperation comprises: taking an average hue of each color light in thefirst converted image, and calculating a difference between the averagehue of each color light and a respective standard hue; and adjusting theprojected first projection image according to the adjustment signal;projecting a second projection image, wherein the second projectionimage comprises a plurality of different color lights and has colorblocks of different brightnesses formed by the plurality of differentcolor lights; capturing the second projection image to generate a secondcaptured image; converting the second captured image into a secondconverted image according to a second conversion matrix; performing thecolor gradation adjustment operation on the second converted image tooutput the adjustment signal, wherein the step of performing the colorgradation adjustment operation comprises: converting each color light ofthe second converted image from the RGB color space to the HSV colorspace, wherein the step of performing the hue adjustment operationcomprises: taking an average hue of each color light in the secondconverted image, and calculating a difference between the average hue ofeach color light and a respective standard hue; and adjusting theprojected second projection image according to the adjustment signal,wherein the step of performing the value adjustment operation comprises:taking the minimum value of each brightness from all color lights of thefirst converted image and the second converted image, and calculating acompensation value of each color light of the first converted image andthe second converted image in such brightness based on the minimum valueof this brightness.